1. Field of the Invention
The present invention relates to a resolver exciter for providing alternating current power to an exciting winding of a resolver.
2. Description of Related Art
A resolver, which includes a stationary exciting winding and a rotating output winding, produces an output voltage in accordance with an angle of rotation of its output winding. The resolver is commonly used in various control devices for detecting angle of rotation.
Normally, a 7 KHz alternating current signal of about 20-30 V must be provided to the exciting winding to drive the resolver. Conventional resolver exciters include a sine wave oscillator, which uses operational amplifiers and the like, and a line driver circuit for amplifying the resulting sine wave oscillating signal and for providing the amplified signal to the exciting winding.
Moreover, when the resolver exciter is to be installed in a vehicle, there is a need to provide a DC/DC converter for boosting the rated voltage (approximately 12 V) of a vehicle-mounted battery to the necessary voltage level.
Meanwhile, as shown in FIG. 3, U.S. Pat. No. 5,304,909 discloses a resolver exciter which includes a sine wave oscillator IC 71, a low-pass filter 72 for filtering the oscillating signal of the IC 71 and a push-pull type line driver circuit 73 for amplifying the filtered signal and for providing the amplified signal to the exciting winding of the resolver.
However, one problem with the above-described conventional resolver exciters is with regards to their costs because they need relatively complicated sine wave oscillators and line driver circuits.
While the device disclosed in U.S. Pat. No. 5,304,909 has a reduced size and a simple circuit construction because of its use of the sine wave oscillating IC, reduction in costs is minimal because this device needs a line driver circuit and a power source for driving the same line driver circuit.